Coulomb’s law & electric fields worksheet with answers

Free printable Coulomb’s law & electric fields worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy
−−1 µC−−4 µCr = 10 cm

Two point charges of −1 µC and −4 µC are 10 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −1 µCq2 = −4 µCr = 10 cm
F = N
2.Easy
−−4 µC−−5 µCr = 2 cm

Two point charges of −4 µC and −5 µC are 2 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −4 µCq2 = −5 µCr = 2 cm
F = N
3.Medium
++3 µC−−3 µCP40 cm

A charge of +3 µC and a charge of −3 µC are 40 cm apart. Point P lies on the line between them, 24 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +3 µCq2 = −3 µCr1 = 24 cmr2 = 16 cm
E = N/C
4.Medium
++8 µC++10 µCP50 cm

A charge of +8 µC and a charge of +10 µC are 50 cm apart. Point P lies on the line between them, 25 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +8 µCq2 = +10 µCr1 = 25 cmr2 = 25 cm
E = N/C
5.Hard
6 cm6 cm+q1​ = +5 µC+q3​ = +5 µC+q2​ = +8 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 5 µC is at the right-angle corner, q₁ = 5 µC is 6 cm from it along one side and q₂ = 8 µC is 6 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 5 µCq2 = 8 µCq3 = 5 µCr13 = 6 cmr23 = 6 cm
F = N
6.Hard
L = 60 cm15°qq

Two identical small balls, each of mass 3 g, hang from the same point on insulating threads 60 cm long. They are given equal charges and each thread settles at 15° from the vertical. Use g = 9.81 m/s². Find the charge q on each ball in nC. Use k = 8.99 × 10⁹ N·m²/C².

m = 3 gL = 60 cmθ = 15°g = 9.81 m/s²
q = nC

Answer key

  1. 1. F = 3.596 N
  2. 2. F = 449.5 N
  3. 3. E = 1.522 × 10⁶ N/C
  4. 4. E = 287680 N/C
  5. 5. F = 117.8 N
  6. 6. q = 290.9 nC

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